The present invention relates to surface alteration by the use of gaseous particles and, more particularly, to apparatus which employs directed neutral atoms for substrate surface removal.
In the semiconductor field, a number of techniques are presently used to etch or otherwise alter substrate surfaces. One of the more commonly used systems is called the barrel etcher. It employs a resident plasma to erode the substrate's surface, which plasma generally exhibits a density of approximately 10.sup.10 cm.sup.-3 at energy levels in the 1-3 eV range. Such barrel etchers are effective but are relatively slow in their action. Moreover, the use of charged particles for etching often tends to charge the substrate being etched, which charge may alter the etch profile, or lead to voltage gradients which may damage the performance of the device.
One modification to the barrel etcher involves the use of a magnetically enhanced plasma wherein the plasma density is increased 10.sup.12 cm.sup.-3 with energy potentials greater than 100 eV. Obviously, the etching rate within such a system is much more rapid; however, substrate surface penetration and damage occurs and additional treatments are required to "heal" such damage. A still further modification to the barrel etcher is called the "after glow" reactor wherein a gas is passed through a microwave discharge to create a plasma. The plasma drifts downstream into a reaction chamber; by the time it reaches the reaction chamber, the plasma has recombined into neutral gas atoms which are then employed to provide isotropic etching. The resulting atoms have very low energies, e.g. on the order of 0.03-0.15 eV.
All of the above systems are designed to overcome the "activation" energy barrier (i.e. the energy required to cause a specific physical or chemical reaction to occur) of the substrate sought to be eroded. Typically, chemical bonds exhibit approximately 5-10 eV energy bond levels. In order to affect those bonds, the activation energy barrier (which is generally some percentage of the chemical bond energy) needs to be exceeded. It is not desirable to greatly exceed the chemical energy bond as this may succeed in inhibiting the chemical bond alteration and potentially damages the surface. For that reason, it is desirable to utilize particles in etch systems which have an energy range in the 1-50 eV range and more preferably in the 1-15 eV range. Furthermore, it is preferable to provide a particle etching system wherein the etch capability is anisotropic and evidences etch aspect ratios in the 20 to 1 range or better.
Accordingly, it is an object of this invention to provide a system for altering the surface of the substrate which employs neutral particles.
It is a further object of this invention to provide a neutral particle surface etcher wherein the energy of the particles impinging upon the surface can be controlled.
It is still another object of this invention to provide a surface etcher which can provide a substantially collimated beam of neutral particles.